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A federal jury found former Goldman Sachs Group Inc. trader Fabrice Tourre liable for misleading investors in a mortgage-linked deal that collapsed during the financial crisis, delivering a historic win for a U.S. regulator eager to prove its mettle inside the courtroom.

The panel of nine jurors reached their verdict Thursday during the second day of deliberations, finding Mr. Tourre liable on six of seven claims that he violated federal securities law.

The victory is an important one for the Securities and Exchange Commission, which has struck out in past efforts to make a convincing case to jurors in high-profile trials against individuals.

For the SEC, the verdict offers a rebuttal to critics who have accused the agency of seeking to make fairly junior employees, such as Mr. Tourre, scapegoats for Wall Street's wider failings.

The civil trial, which began July 15, led jurors through a dense fog of industry jargon, to a time on Wall Street when one era was drawing to a close and the dark clouds of another loomed. The SEC's case centered on a complex mortgage-linked deal between sophisticated investors, and whether Mr. Tourre misled them on the role New York hedge fund Paulson & Co. would play in that instrument.

SEC officials will see their success in such a landmark and controversial lawsuit as vindication of their postcrisis enforcement efforts, including a push to ensure individuals are held to account alongside their employers, according to people close to the agency.

As part of those efforts, the agency has charged 157 firms and individuals to date, securing $2.68 billion in penalties and other sanctions, according to its website. The tally includes 66 chief executives and other senior corporate officers.

Mr. Tourre, who left Wall Street to pursue a doctorate in economics, may face a fine and a ban from the securities industry.

"We're obviously gratified with the jury's verdict and we appreciate their hard work," Matthew Martens, the lead SEC lawyer, after the verdict was delivered.